Evaluation of main traffic congestion degree for restricted waters with AIS reports

Traditionally, marine traffic congestion degree in restricted waters is usually deduced from traffic volume or traffic density. Both of which, however, can not be easily and accurately determined and can not fully reflect the traffic congestion degree. This paper uses the concept of main traffic flow velocity, which varies with the main traffic congestion from a statistics view, to determine the main traffic congestion degree in restricted waters. Main traffic flow velocity can be calculated by averaging the speeds of all ships equipped with an AIS transponder if the percentage of these ships over all vessels in the main traffic is great enough and they are well-distributed, and a fuzzy relationship is established to determine the traffic congestion degree under varying main traffic flow velocity. The concept of main traffic flow velocity provides a more intuitive and accurate way to evaluate the main traffic congestion degree of restricted waters than traffic density and traffic volume in certain situations, and can be easily implement.